电磁屏蔽中的难题—磁场屏蔽

磁场屏蔽是电磁屏蔽中的难点.本文分析了磁场干扰的产生机理,进而分别对高频磁场屏蔽和低频磁场屏蔽进行了分析并提出了一些抑制磁场干扰的措施.     

加固型彩色CRT抗磁场干扰系统

介绍了加固型彩色ＣＲＴ显示器抗磁场干扰系统的设计方案，提出了一种基于自适应干扰对消器的抗磁场干扰方法－－有源自适应磁补偿法。分析了有源自适应磁补偿法的原则，描述了基于８０Ｃ２５１单片机的抗磁场干扰测控系统的硬件结构及软件组成。初步实验结果表明，该系统对外界磁场干扰的抑制能力大于３５ｄＢ。     

计算机机房雷电感应危害计算分析及防护措施研究

计算机机房中有各种各样的电子信息设备,是网络传输枢纽以及数据处理中心,在信息化时代计算机机房的作用十分突出。但是电子信息设备本身具有耐压性能差、抗电磁干扰性能低的问题,雷电作为一种自然现象,产生的强大的电磁感应磁场对计算机机房中的设备产生的危害和影响较大。文章对计算机机房的雷电感应危害计算方法进行分析,并且提出相应的防护措施,旨在加强对计算机机房设备的保护。     

低频脉冲磁场作用下计算机效应的试验研究

低频脉冲磁场是一种常见电磁干扰源，可以在雷电放电、地面核爆炸及生产生活等多种活动中产生，具有低频、低阻和时变等多重特性，可通过直接穿透和磁电感应作用于计算机系统上，对其产生干扰或毁伤.为确定低频脉冲磁场对计算机系统的效应规律，文章利用螺线管脉冲磁场模拟装置，开展了低频脉冲磁场作用下联想品牌计算机（包括2款台式机和一款笔记本）效应的试验研究，得到了扰乱阈值和效应规律，分析了磁场特征参数与效应现象的关系，并与相关研究成果进行了对比.其中脉冲磁场上升时间在数μs至数百μs之间，磁感应强度最大约70 mT.研究结果符合理论预期，并与现有成果逻辑关系一致，可为计算机系统及相近设备的低频脉冲磁场防护提供参考和依据.     

电缆磁耦合分析及磁屏蔽材料应用

对电缆的磁场耦合以及屏蔽层对磁耦合的抑制方式进行了分析,介绍了信号电缆磁耦合干扰抑制的方法,并利用磁性材料研究了信号电缆磁耦合干扰的抑制效果。试验结果表明,非磁性的金属屏蔽层对低频磁耦合干扰无抑制作用,采用减小信号回路面积、电缆外屏蔽层包覆磁性材料的方式,可以屏蔽低频磁场。     

应用于半导体设备的单片机系统中的“看门狗”

随着半导体设备中单片机的应用越来越多,对单片机控制系统的抗磁场干扰性能的要求不断提高,抗磁场干扰性能不仅来自硬件电路而且来自软件的稳定性。本文介绍了提高半导体设备单片机系统可靠性的“看门狗”硬件电路和软件设计方法。     

ADI LTC6813低频抗扰测试解决方案

<正>引言通常汽车零部件受到的磁场干扰可以分为内部或外部干扰源干扰，其中内部干扰源包括汽车的电动马达、制动器等；而外部干扰源包括功率传输线、充电站等。低频磁场抗扰测试MFI的方法是将DUT暴露在干扰磁场中进行测试。辐射环可以产生干扰磁场，还可以用于小型DUT测试，或者采用多点放置的方法来测试大型DUT。本文为大家介绍一种BMS采样板针对低频磁场抗扰测试的解决方案。     

视频显示器的极低频磁场敏感度和辐射测量

视频显示器(VDU)易受极低频(ELF)磁场干扰，但其本身也向周围辐射电场和磁场。VDU的ELF磁场敏感度和辐射程度已经成为衡量其质量和性能的指标之一。给出了5个厂家9种型号共36台VDU的敏感度和辐射测量结果。设计制作了用于测量工频和3次谐波磁场敏感度的实验装置。发现VDU对ELF磁场的敏感度与其刷新频率和外部磁场的方向密切相关。与工频磁场相比，VDU对谐波磁场的敏感度更高。对照有关电磁兼容国际标准对敏感度和辐射测量结果进行了分析。     

人手姿态检测系统的设计与实现

为了增强人机交互的交互性以及遥控操作的可控性,设计并实现了一款基于磁场传感器与微加速度计的人手姿态检测系统。利用坐标变换理论,通过磁场传感器数据解算姿态的翻滚角和俯仰角,然后结合磁场传感器数据解算方位角,并对传感器的噪声、温度漂移以及磁场传感器受外界磁场的干扰进行了补偿。通过实验证明,该系统能准确测量人手姿态。     

印制电路板上的干扰及其抑制方法

在电子电路和电子设备中,由于干扰的存在,会影响电路板的正常工作。文章分析了印制电路板的干扰及抑制,包括电路系统的接地、电源干扰、磁场干扰及热干扰。     

激光等离子体中密度孤波和自生磁场的数值模拟

为了深入理解激光与等离子体相互作用时产生的密度孤波和自生磁场的形成机制,从动力论出发,数值模拟了从波-波、波-粒相互作用出发的轴对称柱坐标下的密度扰动非线性控制方程,得到了密度孤波和自生磁场的形成和演化过程。数值结果表明,强度为4×1014W/cm2的激光打靶时形成的孤波最大密度扰动率达到82%,并产生30T的自生磁场,与实验测量结果相符合,为密度孤波和自生磁场的形成提供了理论依据。     

A survey of electric and magnetic fields among VDT operators inoffices

The ambient electric and magnetic fields as well as the electromagnetic fields associated with video display terminals (VDTs) at 150 offices are measured. The aim of the study is to determine the general level of the various electromagnetic parameters in offices and establish a technical base for a case referent study of skin symptoms among VDT workers. The median value of the 50-Hz background field in the 150 offices is 0.07 μT. Seven of the offices have background levels higher than 0.5 μT, which is high enough to cause distortion of the picture on the screen. The dominant source for electric fields in the ELF range is electric equipment in the office, not the VDTs. The equivalent surface potential is less than 0.5 kV for 63% of the measured VDTs. The computer monitor is a major source of magnetic fields in the offices. The median value of the magnetic field in the ELF range in front of the VDT is 0.21 μT, and in the VLF range it is 0.03 μT     

计算机集群监控系统任务模型的研究

高性能集群系统是目前的研究热点之一，研究高效的集群监控系统，具有重要的现实意义。通过分析集群系统的任务特点，建立了集群监控的任务模型，为监控系统的实现提供了理论上的支持。     

Quaternion-based extended Kalman filter for determining orientation by inertial and magnetic sensing

In this paper, a quaternion based extended Kalman filter (EKF) is developed for determining the orientation of a rigid body from the outputs of a sensor which is configured as the integration of a tri-axis gyro and an aiding system mechanized using a tri-axis accelerometer and a tri-axis magnetometer. The suggested applications are for studies in the field of human movement. In the proposed EKF, the quaternion associated with the body rotation is included in the state vector together with the bias of the aiding system sensors. Moreover, in addition to the in-line procedure of sensor bias compensation, the measurement noise covariance matrix is adapted, to guard against the effects which body motion and temporary magnetic disturbance may have on the reliability of measurements of gravity and earth's magnetic field, respectively. By computer simulations and experimental validation with human hand orientation motion signals, improvements in the accuracy of orientation estimates are demonstrated for the proposed EKF, as compared with filter implementations where either the in-line calibration procedure, the adaptive mechanism for weighting the measurements of the aiding system sensors, or both are not implemented.     

基于USB接口的CAN总线适配器的设计

随着现场总线技术和计算机与外设接口技术的发展，建立现场总线网络节点和监控计算机之间可靠的通讯连接更加重要。对几种接口方法进行了比较，提出了一种使用USB接口实现CAN总线网络与计算机连接的方案，并结合设计实例，论述了系统硬件构成和固件、驱动程序的设计方法。     

Calculating the voltages induced in technological systems during ageomagnetic disturbance

During geomagnetic disturbances voltages are induced in electrically conducting networks such as power systems, pipelines, and phone cables. The voltage produced in a horizontal loop at the Earth's surface can be calculated by considering the changing vertical magnetic field through the loop or by calculating the electric field around the loop from the horizontal magnetic field variations. The two approaches are equivalent, both being a consequence of Maxwell's equations, however, this equivalence is difficult to visualize. By considering the nondivergent nature of the magnetic field, it is shown how the vertical magnetic field through a horizontal loop is related to the horizontal magnetic field at the periphery of the loop. The case of a magnetic disturbance due to a line current above the earth's surface is used to illustrate the equivalence of the two approaches for calculating the voltage induced in a conducting network     

地磁场测量信号处理系统的应用研究

介绍了各向异性磁阻（AMR,Anisotropic MagnetoresistiVe）传感器探测系统对地磁场扰动信号的检测电路的实现及数据信息处理方法。这种利用车辆通过道路时对地球磁场的影响来完成车辆检测的数据采集系统具有常规线圈检测器所不具备的优点,在智能交通系统（ITS）的信息采集中起着非常重要的作用。实测效果直观明显,探测灵敏度达到2mV／V／Oe,线性度误差达到0．05％FS。     

Analog computer solutions for correction of ripple in magnetically-collimated electron beams

Analysis of the dynamics of an electron beam in a magnetic collimating field leads to formulas which can be processed conveniently in an analog computer to obtain individual solutions. This technique is applied to the problem of correcting the ripple which is generally imposed upon the envelope of the beam after passage through a spatial variation or reversal of the collimating field. However, a relatively general viewpoint is retained in developing methods and formulas for studying the motion of an outermost electron of a relatively uniform, round, straight electron beam. Fer this reason the results can be applied to beams from shielded or unshielded cathodes, passing through uniform, periodic, or nonperiodic reversing magnetic collimating fields. A simplified development of the mathematical theory of magnetically confined electron beams is presented, including the effects of spatial variations and reversals in the collimating magnetic fields. Formulas are developed for the equilibrium electron beam radius, and for the ripple frequency, axial wavelength, amplitude, and phase of the outermost electrons, in terms of the field parameters and the initial beam conditions. Analog computer solutions for an electron beam with various collimating magnetic fields serve to illustrate and confirm the developed formulas. From these computer solutions, suggestions are derived for guidance in shaping collimating magnetic fields so that electron beam ripple will be prevented or reduced.     

VCSEL激光器抗干扰温度控制

由于VCSEL具有低功耗、小体积、高调制频率和容易集成等特征,被广泛应用于磁探测领域之中。作为一种高精密的传感器,原子磁强计在测量磁场过程中由于激光器的输出不稳定导致测量精度下降。针对环境等干扰导致激光器的输出不稳定问题,设计了一种可以抵抗环境温度变化的控制器。首先,通过带DSP内核的ADAU1401A芯片与DPSD方法实现了高分辨率温度解算;然后,通过系统辨识的方式建立温控数学模型;最后,应用干扰观测器与内模控制原理设计出抗扰动、低超调、鲁棒性的控制器。实验结果表明:在70 ℃温度下, 存在干扰的控制精度为±0.003 ℃,常温下控制精度为±0.001 5 ℃,为激光器稳定输出与高精度磁场测量奠定了基础。